1. Field of the Invention
This invention relates to a novel composition of matter for reducing cosolvent quantities in water-borne resins. Particularly, this invention relates to a novel composition of matter that has been found to give good film forming characteristics from cosolvent/aqueous media and improved impact resistance. More particularly, this invention relates to a novel water-borne composition that can be reacted to higher molecular weight than standard trimellitic anhydride resins without gelling. The invention composition permits the use of less amounts of environmentally dangerous cosolvents in an aqueous alkyd system.
2. Description of the Prior Art
In water-borne alkyd coatings, the reduction of organic cosolvents is important since they contribute to the amount of volatile organic compounds (VOC's) in the system. Historically, the use of trifunctional acids such as trimellitic anhydride has been the preferred method of solubilizing preformed alkyd resins into an aqueous medium. Alkyd resins are presynthesized to an acid number of about ten and then further reacted with trimellitic anhydride to an acid number of about 45 to 50 to form resins that may be neutralized with base to provide water soluble resins (Amoco Technical Bulletin GSTR 21).
A main deficiency of this technology is the need for a relatively large amount of organic cosolvent in the mixture to maintain solubility. The organic cosolvents that are commonly employed include acetone, butanol, secondary butanol, cyclohexanone, ethylene glycol monobutyl ether, and methyl isopropyl ketone. The chief characteristic of these solvents is that they are at least partially water soluble and have the ability to interact with the water-borne resin to maintain its solubility. Although these water/cosolvent/resin compositions give reasonable properties, the fact that relatively large amounts of cosolvent must be employed means that a large amount of organic material escapes into the environment during processing and application leading to pollution. Although alternative systems to alkyds exist, such as epoxies and acrylics, these latter suffer from deficiencies such as very high price and relative difficulty in application in the case of epoxies and poorer properties with an acrylic.
Therefore, it is the object of this invention to have an alkyd composition that addresses environmental concerns by effectively reducing the amount of cosolvent in the system. In addition, organic cosolvents are frequently expensive and any means of reducing their presence would lead to lowered costs for a paint.